“This paper is an excellent illustration of the international nature of science. The authors have combined a method for programming human stem cells to make kidney tissue, recently developed in Australia, with a technique for transplanting kidney tissue under the skin of mice, developed thirteen years ago in Italy, and a host of tissue analysis techniques developed mainly in the USA, UK and Europe.

“With these techniques, they showed that human kidney tissue developed from human stem cells matures somewhat better grafted into a host animal than it does if left in culture dishes, although it is still far from making a complete kidney. Importantly, they also show that, at least within the limitations of the experiment, the grafted tissue is safe and does not produce tumours – a risk that always worries people doing stem cell work. This is a valuable study; a small but important step that follows previous steps, and that will have to be followed by many more before the work finds direct use in human medicine.”

“In this study the authors started with established human stem cell lines and persuaded them to choose to become kidney cells in the petri dish and then they implanted them in animals and achieved early-stage structures that with better plumbing one can readily imagine turning into functioning kidneys.

“This study bridges the gap between getting stem cells to differentiate into cell types that we need in the lab and actually moving them towards making an organ. For too long there has been hype that inkjet printing of cells and polymers will give us a functioning organ. When thinking about the kidney then it’s not sufficient that the cells should express the right proteins that tells us that they might grow up to be kidney cells one day – they must also form into tubules and work together to become a functioning kidney. That is what is great about this study – they have gone probably as far as anyone can to differentiate the cells into kidney type cells in the laboratory in 2-D and 3-D culture in the petri dish, but then they show that by implanting these human cells under the skin of mice that lack a functioning immune system that the cells self organise into little tubes which are the functional unit of the kidney. This is a key step showing that the cells had the potential – what was needed was to give them an appropriate environment in which they could self organise.

“This study points the way to one day achieving growth of new kidneys to replaced damaged kidneys in patients.”